Question

find the interval of
$( {x}^{2} - 4) \sqrt{ {x}^{2} - 1} < 0$
​

Answer 1

Answer:

Clearly, f(−1)>0,f(2)<0

Now, f(0)=−4<0

⇒f(−1)=1−a−4>0

and f(2)=4+2a−4<0

⇒a<−3 and a<0

⇒a∈(−∞,−3).